The DNA of prehistoric animals and people is being destroyed as a result of museums' handling and storage of fossils, according to a study in the Proceedings of the National Academy of Science.

Samples of 247 fossilized bones from as long as 50,000 years ago from 60 sites in Europe and the Middle East were analyzed for DNA content. DNA was found in freshly dug fossils 46 percent of the time; 18 percent of older fossils yielded DNA.

“The preservation of DNA in these regions is poor due to the climate,” said Eva-Maria Geigl, a molecular biologist at the Institut Jacques Monod in Paris, who led the study. “The less DNA they contain, the more it matters when the tiny amount of DNA that is in there is degraded.”

Ancient DNA, which can remain in fossilized bones for as long as 130,000 years in temperate regions, has been used to investigate the origins of human society – for example, by studying the domestication of animals in the Middle East's Fertile Crescent or mapping the Neanderthal genome, Geigl said.

Freshly excavated bones had six times more DNA than bones that had been cleaned and stored, the study said. In one case, newly excavated fossils were compared with fossils dug up at the same site in 1947. All of the recently unearthed bones had DNA, while no DNA was found in the stored bones.

When dirt and debris are cleaned off the bones, water and chemicals can be absorbed into the fossil, destroying the DNA molecules. Storage in museum warehouses exposes the fossils to heat and oxygen, which can further break down DNA. A fossil moved from a chilly site to a warmer museum warehouse will deteriorate 16 times as quickly, the study said.

“The moment you pull a fossil out of the ground, it starts deteriorating,” said Alan Turner, a researcher at the American Museum of Natural History's division of paleontology in New York. “The sooner that you start looking for ancient DNA once you actually get a fossil, the more it increases your chances.”

DNA for research like Geigl's is hard to find, even in freshly excavated fossils. Half the fossils from Europe have DNA, while warmer areas such as the Middle East have DNA 2 percent of the time. Almost no tropical fossils yield DNA, she said.

While chilling the fossils and packing them in dirt preserved some of her samples, Geigl said it's unrealistic to expect museums to refrigerate all of their bones. Instead, paleontologists, archeologists and molecular biologists can work together to preserve the most interesting fossils for research, she said.

“To understand each other takes a lot of effort, but it's possible, and it certainly also is the way to go for scientific reasons,” Geigl said. “If I don't find DNA, I can't do my research.”

The study was paid for by France's National Center of Scientific Research, Biodiversity Institute and National Space Study Center and Spain's Ministry of Science and Technology.